A bumper skin of a motor vehicle to which various elements such as a reinforcement or a sensor support are added and fastened is already known in the state of the art. One known method of fastening these various elements is staking.
For example, to fasten a reinforcement on a bumper skin, the bumper skin is equipped with a protuberance projecting from its hidden side and a hole is made in the reinforcement. The reinforcement is then placed in contact with the side of the bumper skin that has the protuberance projecting so that the protuberance goes through the hole, leaving an end portion sticking out. The end portion of the protuberance is then fully heated, for example using ultrasound waves generated by a sonotrode, and a rivet head is formed by crushing the protuberance vertically.
This known method of fastening generally involves heating the protuberance along its entire length. The protuberance is often heated and crushed using the same tool which, during heating, is near the upper end of the rib, thereby limiting its movements during crushing. The heating duration is relatively long, so that the heat propagates along the entire length of the protuberance and the protuberance material is completely melted.
In addition, by directing the flow of heat along the vertical direction of the protuberance, there is a risk of heating the side of the bodywork element from which the protuberance is projecting, which may cause appearance faults in this bodywork part.
Lastly, by crushing the protuberance towards the base of the protuberance, i.e. perpendicular to the bodywork element, there is a risk of pressing the surface of this element, thereby causing appearance faults.